The present invention relates to wireless communications apparatus and methods, and more particularly, to wireless communications system and methods using satellite and terrestrial components.
FIG. 1 illustrates a conventional terrestrial wireless communications system 100, and more particularly, a system conforming to the GSM standards. The system 100 includes a mobile switching center (MSC) 110, a base station controller (BSC) 120, and at least one base transceiver station (BTS) 130. The BTS 130 includes radio transceivers that communicate with cellular terminals 50, while the BSC 120 manages radio resources for one or more BTSs and provides a connection between the BTSs and the MSC 110. The MSC 110 typically acts like a telephone switching node, and typically provides additional functions related to registration and mobility management for the cellular terminals 50. The MSC 110 is typically coupled to a public switched telephone network (PSTN) 10, which provides communications links between the cellular terminals 50 served by the wireless system 100 and other terminals (e.g., landline telephones). It will be appreciated that other wireless communications systems may provide similar functionality, but may, for example, use other groupings of functions referred to by different nomenclature.
Cellular satellite communications systems and methods are also widely used to provide wireless communications. Cellular satellite communications systems and methods generally employ at least one space-based component, such as one or more satellites that are configured to wirelessly communicate with a plurality of radiotelephones or other types of cellular terminals. The overall design and operation of cellular satellite communications systems and methods are well known to those having skill in the art, and need not be described further herein.
Hybrids of satellite and terrestrial systems may also be used. For example, as is well known to those having skill in the art, terrestrial networks can enhance cellular satellite communications system availability, efficiency and/or economic viability by terrestrially reusing at least some of the frequency bands that are allocated to cellular satellite communications systems. In particular, it is known that it may be difficult for cellular satellite communications systems to reliably serve densely populated areas, because the satellite signal may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, the satellite spectrum may be underutilized or unutilized in such areas. The use of terrestrial retransmission can reduce or eliminate this problem.
Moreover, the capacity of the overall system can be increased significantly by the introduction of terrestrial retransmission, since terrestrial frequency reuse can be much denser than that of a satellite-only system. In fact, capacity can be enhanced where it may be mostly needed, i.e., densely populated urban/industrial/commercial areas. As a result, the overall system can become much more economically viable, as it may be able to serve a much larger subscriber base. One example of terrestrial reuse of satellite frequencies is described in U.S. Pat. No. 5,937,332 to the present inventor Karabinis entitled Satellite Telecommunications Repeaters and Retransmission Methods.